User apparatus, and preamble transmission method

ABSTRACT

A user apparatus in a radio communication system including a base station and the user apparatus, including: a reception unit configured to receive a plurality of predetermined signals transmitted from the base station by a plurality of beams; and a transmission unit configured to transmit a preamble using a resource corresponding to at least one beam of the plurality of beams, wherein the reception unit measures a reception quality for each of the plurality of beams, and the transmission unit transmits the preamble using a resource corresponding to a beam of a reception quality that satisfies a predetermined condition.

TECHNICAL FIELD

The present invention relates to a user apparatus and a base station ina radio communication system.

BACKGROUND ART

In LTE (Long Term Evolution), random access (RA: Random Access) isperformed when a user apparatus establishes a connection with a basestation, or performs resynchronization (Non-Patent Document 1).

In 3GPP (3rd Generation Partnership Project), study of a radiocommunication scheme called 5G has been progressing for realizingfurther increase of system capacity, further increase of datatransmission speed, and lower delay in radio sections and the like. In5G, in order to satisfy the requirement to make the delay of the radiosection equal to or less than 1 ms while realizing throughput equal toor greater than 10 Gbps, studies of various radio techniques areprogressing. Since there is a high possibility in that radio techniquesdifferent from LTE are adopted in 5G, a radio network supporting 5G iscalled a new radio network (NR: New Radio) so that 5G is differentiatedfrom a radio network supporting LTE in 3GPP. Note that NewRAT may bereferred to as NR.

In 5 G, it is assumed that a wide range of frequency from a lowfrequency band similar to LTE to a frequency band higher than that ofLTE is used. Especially, in the high frequency band, since propagationloss increases, it is being studied to apply beam forming of narrow beamwidth in order to compensate it.

PRIOR ART DOCUMENT Non-Patent Document

[Non-Patent Document 1] 3GPP TS 36.321 V14.0.0 (2016-09)

SUMMARY OF INVENTION Problem to be Solved by the Invention

It is considered that in the case of transmitting a signal by applyingbeamforming, the base station or the user apparatus determines thedirection of a transmission beam (Tx-beam) such that reception qualitybecomes good in the communication partner side by performing beam search(beam sweeping) or the like. In the same way, it is considered that inthe case of receiving a signal by applying beamforming, the base stationor the user apparatus determines the direction of a reception beam(Rx-beam) such that reception quality from the communication partnerside becomes good.

Here, also in NR, it is assumed that a random access procedure similarto the random access procedure in LTE is performed. However, in NR, itis being studied to apply beamforming as described above also in therandom access procedure.

However, in the case in which beamforming is applied in the randomaccess procedure, for example, when the user apparatus detects aplurality of base station side transmission beams, for which basestation side transmission beam a RA preamble to transmit or the like isnot clear in the conventional technique. In the conventional technique,there is a possibility that the random access procedure cannot beappropriately executed in the radio communication system to whichbeamforming is applied.

The present invention is made in view of the above-described points, andan object of the present invention is to provide a technique thatenables a radio communication system having a user apparatus and a basestation to appropriately execute a random access procedure to whichbeamforming is applied.

Means for Solving the Problem

According to a disclosed technique, there is provided a user apparatusin a radio communication system including a base station and the userapparatus, including:

a reception unit configured to receive a plurality of predeterminedsignals transmitted from the base station by a plurality of beams; and

a transmission unit configured to transmit a preamble using a resourcecorresponding to at least one beam of the plurality of beams,

wherein the reception unit measures a reception quality for each of theplurality of beams, and the transmission unit transmits the preambleusing a resource corresponding to a beam of a reception quality thatsatisfies a predetermined condition.

Advantage of the Invention

According to a disclosed technique, there is provided a technique thatenables a radio communication system having a user apparatus and a basestation to appropriately execute a random access procedure to whichbeamforming is applied.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a radio communication system in anembodiment of the present invention;

FIG. 2 is a diagram for explaining an example of a random accessprocedure;

FIG. 3 is a diagram for explaining beams transmitted from the basestation 20;

FIG. 4 is a diagram for explaining a transmission method of a RApreamble;

FIG. 5 is a diagram for explaining an operation example in a case inwhich the user apparatus 10 receives a plurality of pieces of basicbroadcast information/SS;

FIG. 6 is a diagram for explaining an embodiment 1;

FIG. 7 is a sequence diagram for transmitting a threshold from the basestation 20 to the user apparatus 10;

FIG. 8 is a diagram for explaining an application method of a threshold;

FIG. 9 is a diagram for explaining an example in the case in which athreshold is applied in retransmission;

FIG. 10 is a diagram for explaining an example in the case in which theRAR window is divided in the time direction in the embodiment 2;

FIG. 11 is a diagram for explaining an example in the case in which theRAR window is divided in the frequency direction in the embodiment 2;

FIG. 12 is a diagram for explaining the case in which a common RARwindow is used in the embodiment 2;

FIG. 13 is a diagram showing an example of a functional configuration ofthe user apparatus 10;

FIG. 14 is a diagram showing an example of a functional configuration ofthe base station 20;

FIG. 15 is a diagram showing an example of a hardware configuration ofthe user apparatus 10 and the base station 20.

EMBODIMENTS OF THE INVENTION

Hereinafter, an embodiment of the present invention (present embodiment)will be described with reference to the accompanying drawings. Theembodiments described below are only examples and embodiments to whichthe present invention is applied are not limited to the followingembodiments.

In actual operation of the radio communication system of the presentembodiment, existing techniques can be appropriately used. The existingtechniques are techniques of LTE, for example, but not limited to LTE.In addition, “LTE” used in this specification has a broad meaningincluding LTE-Advanced and schemes after LTE-Advanced (example: 5G)unless otherwise specified.

In the following embodiment described below, terms RA preamble, RAR,messages 1-4, RAR window, SIB, and the like which are used in theexisting LTE are used, but these terms are only used in convenience ofdescription, signals or functions and the like similar to signals orfunctions indicated by the terms may be referred to as other names.

Also, in the present embodiment, a random access procedure based on therandom access procedure prescribed in LTE is taken as an example.However, the application destination of the present invention is notlimited to the random access procedure. The present invention is alsoapplicable to communication procedures other than the random accessprocedure.

Also, selecting basic broadcast information/SS associated with a beamcan be considered to be synonymous with selecting the beam.

In the following description, embodiments 1 and 2 are described. Beforedescribing the embodiments 1 and 2, a basic example as a technology as apremise of the embodiments 1 and 2 is described. Embodiments 1 and 2 aredescribed as improvement measures against the basic example.

Basic Example

<System Whole Configuration>

FIG. 1 shows a block diagram of a radio communication system in thepresent embodiment. The radio communication system of the presentembodiment includes a user apparatus 10 and a base station 20 as shownin FIG. 1. In FIG. 1, one user apparatus 10 and one base station 20 areshown, but this is an example and a plurality of user apparatuses 10 anda plurality of base stations 20 may exist.

The user apparatus 10 is a communication apparatus having a radiocommunication function such as a smartphone, a mobile phone, a tablet, awearable terminal, a communication module for M2M (Machine-to-Machine),and the like, and the user apparatus 10 connects to the base station 20by radio to use various communication services provided by the radiocommunication system. The base station 20 is a communication apparatusthat provides one or more cells and performs radio communication withthe user apparatus 10. Both of the user apparatus 10 and the basestation 20 can perform beamforming to transmit and receive signals.

In the present embodiment, the duplex mode may be TDD (Time DivisionDuplex) mode or FDD (Frequency Division Duplex) mode.

In the following description, transmitting a signal using a transmissionbeam is synonymous with sending a signal multiplied by a precodingvector (precoded with a precoding vector). Similarly, receiving a signalusing a reception beam is synonymous with multiplying a received signalby a predetermined weight vector. Also, transmitting a signal using atransmission beam may be expressed as sending a signal by using aspecific antenna port. Similarly, receiving a signal using a receptionbeam may be expressed as receiving a signal by using a specific antennaport. Note that an antenna port indicates a logical antenna port definedin the standard of 3GPP. Note that methods for forming the transmissionbeam and the reception beam are not limited to those described above.For example, a method for changing an angle of each antenna may be usedin the user apparatus 10/base station 20 having a plurality of antennas,a method for combining the method using the precoding vector and themethod for changing the angle of the antenna may be used, and othermethods may be used.

In the following, a beam used for signal transmission from the basestation 20 is referred to as a BS transmission beam, a beam used forsignal reception by the base station 20 is referred to as a BS receptionbeam, a beam used for signal transmission from the user apparatus 10 isreferred to as a UE transmission beam, and a beam used for signalreception by the user apparatus 10 is referred to as a UE receptionbeam.

<On Random Access Procedure>

An example of a random access procedure in the present embodiment isdescribed with reference to FIG. 2. In the present embodiment, as anexample, a random access procedure similar to the random accessprocedure in LTE is executed (Non-Patent Document 1). In transmissionand reception of signals in the random access procedure, each of theuser apparatus 10 and the base station 20 applies a transmission beamand a reception beam. Note that a part of signal transmission andreceptions may be omnibus transmission/reception.

The base station 20 performs beam sweeping and transmits basic broadcastinformation and a synchronization signal (SS: synchronization signal,hereinafter referred to as SS) at predetermined periods respectively foreach BS transmission beam (step S101). The transmission periods of thebasic broadcast information and the synchronization signal may be thesame or may be different. SIB (System Information Block) described lateris also transmitted at a predetermined period for each BS transmissionbeam. SIB may be referred to as “system information”. In the basicexample, the transmission period of the SIB is longer than thetransmission periods of the basic broadcast information and thesynchronization signal, and the size of the SIB is greater than the sizeof any one of the basic broadcast information and the synchronizationsignal.

FIG. 3 shows an image of BS transmission beams. In the example of FIG.3, three transmission beams of A, B and C are shown. In each of thethree BS transmission beams, basic broadcast information, a SS, a SIB,and the like are transmitted. In the beam sweeping, for example, BStransmission beams are switched for each time (example: for eachsymbol).

The basic broadcast information is, for example, basic systeminformation (corresponding to MIB in LTE) transmitted on a PBCH. The SSincludes, for example, two types of signals (code sequences) of P-SS andS-SS. The P-SS is a signal for the purpose of symbol timingsynchronization, for example, and the S-SS is a signal for the purposeof radio frame synchronization or the like, for example.

By receiving basic broadcast information or a SS or “basic broadcastinformation and SS” by a BS transmission beam, the user apparatus 10 canidentify the BS transmission beam. To identify a BS transmission beamis, for example, to detect an identifier (ID) of the BS transmissionbeam. An ID of a BS transmission beam may be an antenna port number. Forexample, an ID of a BS transmission beam may be included in basicbroadcast information or may be included in a SS. Also, the ID of the BStransmission beam may be associated with a resource (resource of timeand/or frequency) by which the basic broadcast information or the SS istransmitted, so that the user apparatus may identify the BS transmissionbeam by the resource with which the basic broadcast information or theSS is received.

A block that includes any of P-SS, S-SS and basic broadcast informationmay be referred to as an SS-block. The user apparatus 10 may assume thatto receive an SS block transmitted from the base station 20 (toascertain content of the SS block) is to identify the BS transmissionbeam associated with the SS block. In this case, for example, the userapparatus 10 identifies an ID of the BS transmission beam from thecontent of the received SS block or from the resource with which the SSblock is received.

In the case where a resource of a SS block is associated with a BStransmission beam, it is not necessary that the “ID of BS transmissionbeam” to be identified by the user apparatus 10 is an ID assigned forthe BS transmission beam (this is referred to as “beam ID”). Forexample, a time position (Example: symbol index) of the above SS blockis associated with the BS transmission beam and is associated with aRACH resource subset which is a resource used to transmit a RA preamble.In this case, the time position (Example: symbol index) can beconsidered to be the “ID of BS transmission beam”. In this case, it isonly necessary for the user apparatus 10 to recognize the time position(Example: symbol index) of the SS block. Also, in this case, forexample, the beam ID may be included in the basic broadcast information.

That the resource of the SS block is associated with the BS transmissionbeam means that, for example, in the case where there are a BStransmission beam A and a BS transmission beam B, the same BStransmission beam A is used at a symbol A and the same BS transmissionbeam B is used at a symbol B every time at a period of a time unit.

When the resource of the SS block is not associated with the BStransmission beam, for example, the base station 20 includes the beam IDin the basic broadcast information and transmits it, so that the userapparatus 10 identifies the BS transmission beam by reading the beam IDtransmitted by the basic broadcast information.

The technique in this embodiment can be applied to either of the abovetwo patterns. In step S102 of FIG. 2, the user apparatus 10 transmits aRA preamble (Message 1) using a resource (which is referred to as a RACHresource subset) corresponding to a BS transmission beam of the basicbroadcast information and/or the SS (which is represented as “basicbroadcast information/SS”) that can be received in step S101.

Upon detecting the RA preamble, the base station 20 transmits a RAresponse (RAR, Message 2) as a response of the RA preamble to the userapparatus 10 (step S103). The user apparatus 10 that receives the RAresponse transmits a Message 3 including predetermined information tothe base station 20 (step S104). The Message 3 is, for example, an RRCconnection request.

The base station 20 that receives the Message 3 transmits a Message 4(example: RRC connection setup) to the user apparatus 10. After the userapparatus 10 confirms that predetermined information is included in theMessage 4, the user apparatus 10 recognizes that the Message 4 is aMessage 4 that corresponds to the Message 3 and that is addressed to theuser apparatus 10 itself, then the user apparatus 10 completes therandom access procedure. On the other hand, when the user apparatus 10cannot identify the predetermined information in the Message 4, the userapparatus 10 regards it as failure of random access, so that the userapparatus 10 executes the procedure from transmission of a RA preambleagain.

<On Transmission Method of RA Preamble>

An example of a transmission method of RA preamble in the step S102 isdescribed in more detail.

In the present embodiment, the user apparatus 10 selects basic broadcastinformation/SS that can be received among a plurality of pieces of basicbroadcast information/SS transmitted by applying beam sweeping from thebase station 20. This is the same as selecting a BS transmission beamthat transmits the received basic broadcast information/SS. “Received”here means that, for example, it is received with good receptionquality, but it is not limited to this.

In the present embodiment, a BS transmission beam from the base station20 and a RACH resource subset which is a resource to be used fortransmitting a RA preamble from the user apparatus 10 are associatedwith each other. The user apparatus 10 transmits a RA preamble using aRACH resource subset corresponding to a selected BS transmission beam.

As an example, FIG. 4 shows A, B, and C as RACH resource subsets in theside of the user apparatus 10. The RACH resource subsets A, B, Ccorrespond to the BS transmission beams A, B, C as shown in FIG. 3respectively, for example. In FIG. 4, a plurality of RACH resourcesubsets are associated with each BS transmission beam by being dividedin the time direction, but this is only an example. A plurality of RACHresource subsets may be associated with each BS transmission beam bybeing divided in the frequency direction, or a plurality of RACHresource subsets may be associated with each BS transmission beam bybeing divided in units of time and frequency.

The example of FIG. 4 indicates that the user apparatus 10 can receivebasic broadcast information/SS transmitted with the BS transmission beamB, thus, the user apparatus 10 transmits a RA preamble using the RACHresource subset B corresponding to the BS transmission beam B.

Based on a resource of the RA preamble received from the user apparatus10, the base station 20 can determine basic broadcast information/SS (BStransmission beam) received by the user apparatus 10. In the example ofFIG. 4, since the base station 20 receives a RA preamble by the RACHresource subset B, the base station 20 can determine that the BStransmission beam B corresponding to the RACH resource subset B is aproper BS transmission beam that the user apparatus 10 can receive. Forexample, the base station 20 can use the BS transmission beam B insignal transmission to the user apparatus 10 after that. Note that, inFIG. 4, beams indicated by E, F and G in the base station 20 sideindicates BS reception beams, and in this example, as shown in thefigure, it is shown that the base station 20 is performing beam sweepingin the reception side.

Also, FIG. 4 shows a RAR window. In the present embodiment, similarly tothe existing LTE, when the user apparatus 10 that transmits a RApreamble monitors a RA response, but does not receive the RA responsewithin a predetermined time indicated by the RAR window, it isdetermined that the random access fails. However, this is an example,and processing different from that of the existing LTE may be performedas processing for determining whether the RA response is successfullyreceived.

The example of FIG. 4 shows a case where the user apparatus 10 canreceive the basic broadcast information/SS by using one BS transmissionbeam. Or the example of FIG. 4 shows a case where the user apparatus 10can receive the basic broadcast information/SS using a plurality of BStransmission beams, and selects one BS transmission beam that can bereceived the best (example: reception quality is the best) from theplurality of BS transmission beams.

When the user apparatus 10 receives basic broadcast information/SS by aplurality of BS transmission beams, the user apparatus 10 may transmitRA preambles using a plurality of RACH resource subsets corresponding tothe plurality of BS transmission beams respectively. By transmitting theRA preambles by using a plurality of RACH resource subsets, diversityeffect can be obtained.

For example, when there are a plurality of BS transmission beams bywhich the basic broadcast information/SS (or the reference signal) canbe received with good reception quality to the same degree, the userapparatus 10 selects the plurality of BS transmission beams, andtransmits a RA preamble by each of a plurality of RACH resource subsetscorresponding to the plurality of BS transmission beams. Accordingly,the base station 20 may be able to detect a truly optimal BStransmission beam. Also, since it can be considered that UE transmissionbeams and/or BS reception beams may be different between a plurality ofRACH resource subsets, the base station 20 may be able to receive the RApreamble with the optimal beam.

FIG. 5 shows, as an example, a case in which the user apparatus 10transmits RA preambles using RACH resource subsets B and C correspondingto BS transmission beams B and C. Note that when transmitting a RApreamble in each of a plurality of RACH resource subsets, the content(sequence) of the RA preambles may be the same or different among theplurality of RACH resource subsets.

<On Method for Notifying of RACH Resource Subsets>

In the present embodiment, the base station 20 transmits informationindicating a RACH resource subset corresponding to a BS transmissionbeam to the user apparatus 10. Based on the information, the userapparatus 10 can know a RACH resource subset corresponding to a BStransmission beam of received basic broadcast information/SS. As anexample, in the case in which the user apparatus 10 receives from thebase station 20 information indicating a RACH resource subset A as aRACH resource subset corresponding to a BS transmission beam A, if theuser apparatus 10 selects the BS transmission beam A to transmit a RApreamble, the user apparatus 10 transmits the RA preamble using the RACHresource subset A.

“Information indicating a RACH resource subset” notified from the basestation 20 to the user apparatus 10 may be information indicating atime/frequency resource of the RACH resource subset (example: a resourceindex), or information indicating a time resource of the RACH resourcesubset (time position), or may be other information.

For example, the above information is notified, for each BS transmissionbeam, using a SIB transmitted by the BS transmission beam. Also, in aSIB transmitted by a BS transmission beam, information of a RACHresource subset corresponding to another BS transmission beam may beincluded.

<On Transmitting a Plurality of RA Preambles>

From the viewpoint of quickly connecting to the base station 20, it canbe considered that the user apparatus 10 freely transmits a plurality ofRA preambles using the RACH resource subsets associated with each of theplurality of basic broadcast information/SS that can be detected.However, in that case, there is a possibility in that the user apparatus10 transmits the RA preamble using the RACH resource subset associatedwith the basic broadcast information/SS that cannot be received with anappropriate reception quality.

For example, if the user apparatus 10 receives two SSs and there is alarge difference in reception quality between them, the probability thatthe RA preamble transmitted in the RACH resource subset corresponding tothe SS of bad reception quality is successfully received by the basestation 20 side is low. Also, the probability that the RA preamble isnot useful is high from the viewpoint of appropriateness of UEtransmission beam and BS reception beam. Also, by performing RA preambletransmission which is not useful as described above, it will spreadinterference to the surroundings. Further, if the RA preamblecorresponding to the worse reception quality is received by the basestation 20 and the subsequent processing is also continued, thepossibility that the BS transmission beam is not appropriate is high, sothat there is a possibility that the performance of the subsequentcommunication deteriorates.

In particular, the effect is more conspicuous in cases where there isBS/UE beam correspondence, that is, the channel reciprocity is availableon the BS/UE side.

Outline of Embodiments

Therefore, in the embodiments described below, a threshold related tothe reception quality of the BS transmission beam is provided.Basically, when the reception quality of the BS transmission beam in theuser apparatus 10 is better than the threshold, a RA preamble istransmitted using the RACH resource subset associated with the BStransmission beam.

The reception quality is not limited to a particular one. For example,the reception quality is received power of a desired signal receivedfrom the base station 20 by the user apparatus 10, a ratio ofinterference and the received power (received power/interference,so-called SNR), or a ratio of “interferences+noise” and received power(received power/(interference+noise), so-called SINR). Also, thereceived quality may be a pathloss related to the BS transmission beam.The above desired signal is, for example, basic broadcastinformation/SS, a reference signal, or a data signal transmitted by thetarget BS transmission beam.

As described above, when using the received power or a value having thereceived power as numerator as a reception quality, if the value of thereception quality is large, the reception quality is good. On the otherhand, when using the pathloss as the reception quality, if the value ofthe pathloss is small, the reception quality is good. That is, dependingon the type of the reception quality for use, there are a case in whichthe greater (the value) the reception quality is, the better thereception quality is, and a case in which the smaller (the value) thereception quality is, the better the reception quality is.

In this embodiment, “greater than” or “smaller than” may be replacedwith “greater than or equal to” and “smaller than or equal to”.

Hereinafter, for convenience of explanation, the reception quality isdescribed as being better as the value is greater like the receivedpower, for example. As to reception quality that becomes better as thevalue becomes smaller, “greater than” in the following explanation maybe replaced with “smaller than”. Also, In some cases, the expression“reception quality is better than the threshold” is used as anexpression that includes these.

In the following, various examples using a threshold are described as anembodiment 1. Also, variations related to RAR window based on theembodiment 1 is described as an embodiment 2. In the explanation ofembodiments 1 and 2, improvement parts (that is, the change parts) ofthe technique of the basic example described so far are described, andtherefore, in the case where explanation is not particularly given, thebasic example is applied basically.

Embodiment 1

As described above, in the present embodiment, a threshold on thereception quality of the BS transmission beam is provided, andbasically, when the reception quality of the BS transmission beam in theuser apparatus 10 satisfies a predetermined condition, the userapparatus 10 transmits a RA preamble using a RACH resource subsetassociated with the BS transmission beam (basic broadcastinformation/SS). Specific examples of the predetermined conditions aredescribed below, but the predetermined conditions are not limited to thefollowing examples.

As an example, the predetermined condition is that the reception qualityis greater than a threshold. For example, in the case in which thethreshold is TH, if the reception quality X in the BS transmission beamB shown in FIG. 5 is above TH and the reception quality Y in the BStransmission beam C is smaller than TH, the user apparatus 10 transmitsa RA preamble using a RACH resource subset associated with the BStransmission beam B.

For example, the user apparatus 10 applies the above threshold to alldetected BS transmission beams. Also, the user apparatus 10 may applythe threshold only for the BS transmission beams of reception qualityafter the N-th best reception quality by arranging reception qualitiesof the detected plurality of BS transmission beams in descending orderof goodness of reception quality. For example, in the example of FIG. 5described above, if X>Y and N is 2, the user apparatus 10 applies thethreshold only to the BS transmission beam C. That is, the userapparatus 10 applies the threshold only for the second best BStransmission beam C.

Also, the threshold may be different for each BS transmission beam. Forexample, in the example of FIG. 5, TH1 is used for the reception qualityX in the BS transmission beam B, and TH2 is used for the receptionquality X in the BS transmission beam C. When using different thresholdsfor each BS transmission beam, for example, the greater the receptionquality is, the greater the threshold value for use is.

The threshold may be a value (which is referred to as “direct comparisonthreshold”) directly used for comparison with the reception quality asmentioned above, or may be a relative value (which is referred to as“relative threshold”). As to the threshold as the relative value, forexample, the user apparatus 10 compares the relative threshold with adifference that is obtained by subtracting the reception quality in theBS transmission beam of determination target from the greatest receptionquality in reception qualities of the plurality of BS transmissionbeams, and when the difference is smaller than the relative threshold,the user apparatus 10 determines that the user apparatus 10 can transmitthe RA preamble by using the RACH resource subset associated with the BStransmission beam of the determination target.

An example of this case is described with reference to FIG. 6. In theexample of FIG. 6, the relative threshold is 3. For example, the userapparatus 10 measures a reception quality of basic broadcastinformation/SS transmitted by the BS transmission beam B as X, andmeasures a reception quality of basic broadcast information/SStransmitted by the BS transmission beam C as Y. Since X>Y is satisfied,the reception quality of the basic broadcast information/SS transmittedby the BS transmission beam B is the greatest. The user apparatus 10transmits a RA preamble using a RACH resource subset associated with theBS transmission beam B. Also, the user apparatus 10 compares (X−Y) with3, and if (X−Y)<3 is satisfied, the user apparatus 10 transmits a RApreamble using the RACH resource subset associated with the BStransmission beam C.

In the above example, the direct comparison threshold may be applied forthe first RA preamble.

An upper limit value may be set for the number of RA preambles that canbe sent simultaneously (that is, the number of concurrently availableRACH resource subsets). Note that “simultaneous” means a time intervalthat can be regarded as “simultaneous”.

For example, in the case in which the direct comparison threshold isused, when 3 is given as an upper limit value, even if there are four BStransmission beams whose reception quality is greater than the directcomparison threshold, the number of RA preambles that can besimultaneously transmitted is three. In this case, for example, a RApreamble for a BS transmission beam of the worst reception quality amongthe four is not transmitted.

Also, for example, in the case of using the relative threshold describedwith reference to FIG. 6, it is assumed that there are N BS transmissionbeams (including BS transmission beam of the greatest reception quality)having reception quality between the greatest reception quality and(greatest reception quality—relative threshold). If there is no upperlimit value, or the upper limit value is greater than N, N RA preamblesare transmitted. On the other hand, for example, if the upper limitvalue is M(<N), M RA preambles are transmitted.

<As to Threshold>

The above-mentioned threshold (direct comparison threshold, relativethreshold) is, for example, notified by a DCI, a MAC signal, a RRCsignal and the like from the base station 20 to the user apparatus 10.Or, the threshold may be preconfigured in the base station 20 and theuser apparatus 10.

FIG. 7 shows a sequence diagram when transmitting the threshold from thebase station 20 to the user apparatus 10. As shown in FIG. 7, the basestation 20 transmits the threshold to the user apparatus 10 (step S201).The user apparatus 10 holds the threshold in a storage unit such as amemory. Also, the user apparatus 10 determines availability oftransmission of RA preamble for basic broadcast information/SS (BStransmission beam) that can be received by using reception quality inthe BS transmission beam and the threshold, and if the transmission isavailable, the user apparatus 10 performs transmission (step S202).

<Application of Threshold on Retransmission>

In the present embodiment, like the existing LTE, a RAR window (timewindow) is provided. After transmitting a RA preamble, the userapparatus 10 monitors a RAR (RACH response) in the RAR window. Morespecifically, the user apparatus 10 performs blind decoding using aRA-RNTI. After transmitting a RA preamble, if the user apparatus 10 doesnot receive a RAR corresponding to the RA preamble within the RARwindow, the user apparatus 10 performs retransmission of the RApreamble.

As to the threshold already described, it may be applied by the samemethod for initial transmission and retransmission (includingretransmission on or after second retransmission) of a RA preamble. Theuser apparatus 10 may transmit a RA preamble without applying athreshold in the initial transmission, and may apply the threshold inthe retransmission. Also, the user apparatus 10 may not apply thethreshold for RA preambles up to N-th transmission (N is an integerequal to or greater than 1) including initial transmission, and mayapply a threshold when determining transmission of the RA preamble after(N+1)-th transmission (including (N+1)-th transmission). Also, the userapparatus 10 may apply the threshold for RA preambles up to N-thtransmission (N is an integer equal to or greater than 1) includinginitial transmission, and may not apply a threshold when determiningtransmission of RA preamble after (N+1)-th transmission (including(N+1)-th transmission). For example, when N=1, the threshold is appliedin the initial transmission, and the threshold is not applied inretransmission after that.

The above N is, for example, notified by a DCI, a MAC signal, a RRCsignal and the like from the base station 20 to the user apparatus 10.Or, the N may be preconfigured in the base station 20 and the userapparatus 10.

As to the reception quality, a reception quality measured at a timingwhen a RA preamble is transmitted (just before transmission in fact) maybe used, or, when the time interval between initial transmission (orprevious retransmission) and retransmission is short, a receptionquality measured in the initial transmission (or previousretransmission) may be used for determination of retransmission.

The example shown in FIG. 8 shows the case when N=1. As shown in FIG. 8,the user apparatus 10 applies the threshold when performing firstretransmission without applying the threshold in initial transmission.

When performing retransmission, there is a case where the user apparatus10 transmits a RA preamble using a RACH resource subset different from aRACH resource subset for initial transmission (or previousretransmission). For example, at the time of initial transmission, theuser apparatus 10 transmits the RA preamble using a RACH resource subsetcorresponding to the BS transmission beam A as one of the detected BStransmission beams, however, since the RAR cannot be received, the userapparatus 10 transmits a RA preamble using a RACH resource subsetcorresponding to the BS transmission beam B, which is another beam amongthe plurality of detected BS transmission beams in retransmission. Insuch a case, the user apparatus 10 may determine, by using a threshold,whether to change RACH resource subsets between RA preamble transmissionand next RA preamble transmission as retransmission for the RA preambletransmission.

A specific example is described with reference to FIG. 9. First, a casein which the direct comparison threshold TH is used is described. Forexample, by detecting that a reception quality in the BS transmissionbeam B is greater than TH, the user apparatus 10 transmits (initialtransmission) a RA preamble using the RACH resource subset B associatedwith the BS transmission beam B (initial transmission).

The user apparatus 10 decides to retransmit a RA preamble using anotherRACH resource subset because it has sent a RA preamble using RACHresource subset B but did not receive the RAR in the RAR window. In thiscase, for example, the user apparatus 10 detects the BS transmissionbeam C as a BS transmission beam with reception quality above TH, otherthan the BS transmission beam B. More specifically, for example, theuser apparatus 10 detects that basic broadcast/SS associated with the BStransmission beam C can be received with reception quality greater thanTH. Then, the user apparatus 10 retransmits a RA preamble using the RACHresource subset C associated with the BS transmission beam C.

Next, a case in which the relative threshold RTH is used is described.The user apparatus 10 decides to retransmit the RA preamble usinganother RACH resource subset because it has sent the RA preamble usingRACH resource subset B corresponding to the BS transmission beam B butdid not receive the RAR in the RAR window.

Here, it is assumed that the reception quality in the BS transmissionbeam B is B. For example, the user apparatus 10 detects the BStransmission beam C as a BS transmission beam whose reception quality isgreater than (B-RTH). Then, the user apparatus 10 retransmits a RApreamble using the RACH resource subset C associated with the BStransmission beam C.

As described above, in this embodiment, since the transmission of the RApreamble is limited by using the threshold, possibility of improper beamselection that may occur by transmitting a RA preamble using a RACHresource subset corresponding to a BS transmission beam whose receptionquality is not good can be decreased, and interference to surroundingscan be decreased.

Embodiment 2

Next, an embodiment 2 is described. The embodiment 2 is based on thepremise of the embodiment 1 (transmission restriction of RA preambleusing threshold). However, it is not necessary to assume that theembodiment 1 is a prerequisite, and only the basic example can beassumed. In the embodiment 2, a setting example of RAR window isdescribed. In the following, an embodiment 2-1 and an embodiment 2-2 aredescribed.

Embodiment 2-1

In the embodiment 2-1, a RAR window is configured for each of aplurality of RACH resource subsets corresponding to different BStransmission beams.

FIG. 10 shows an example of a case in which RAR windows for each of aplurality of RACH resource subsets are configured by dividing a RARwindow in the time direction. In the case of FIG. 10, a RAR window B isconfigured for the RACH resource subset B by which a RA preamble istransmitted, and a RAR window C is configured for the RACH resourcesubset C by which a RA preamble is transmitted.

For example, by setting, in the user apparatus 10, a time length (to bereferred to as “offset” for convenience sake) from the timing (time)when the RA preamble is transmitted to a start timing (time) of the RARwindow corresponding to the RACH resource subset by which the RApreamble is transmitted, and a time length (to be referred to as “windowtime length” for convenience sake) of the RAR window, the user apparatus10 can determine the RAR window corresponding to the RA preamble basedon the offset and the window time length. Also, the base station 20holds the offset and the window time length, so that the base station 20can specify the RAR window that is used by the user apparatus 10 basedon the timing at which the RA preamble is received.

The above-mentioned offset and the window time length may be notified bya DCI, a MAC signal, a RRC signal and the like from the base station 20to the user apparatus 10, or, may be preconfigured in the base station20 and the user apparatus 10.

FIG. 11 shows an example of a case in which RAR windows for each of aplurality of RACH resource subsets are configured by dividing a RARwindow in the frequency direction. In the case of FIG. 11, a RAR windowB is configured for the RACH resource subset B by which a RA preamble istransmitted, and a RAR window C is configured for the RACH resourcesubset C by which a RA preamble is transmitted.

For example, by setting, in the user apparatus 10, correspondencerelationship between RA preamble transmission timing and a frequencyposition (example: center frequency and width), the user apparatus 10can determine the RAR window based on the timing when transmitting theRA preamble and the correspondence relationship. As to the position(start timing and time length) of the RAR window in the time direction,for example, a start timing and the time length with respect to apredetermined number of RACH resource subsets (example: three RACHresource subsets A, B and C shown in FIG. 11) are fixedly determined forthe predetermined number of RACH resource subsets as common values, sothat they are used. Or, the method described with reference to FIG. 10may be applied for the time direction in the method shown in FIG. 11.

The information indicating the correspondence relationship between theRA preamble transmission timing and the frequency position may benotified by a DCI, a MAC signal, a RRC signal and the like from the basestation 20 to the user apparatus 10, or, may be preconfigured in thebase station 20 and the user apparatus 10.

In the embodiment 2-1, for example, a plurality of RAR windowscorresponding to a plurality of RA preamble transmissions are configuredsuch that they do not overlap. Accordingly, the user apparatus 10 candetermine that which RACH resource subset (that is, which BStransmission beam) the received RAR corresponds to based on the RARwindow in which the RAR is received. As described above, by configuringthe plurality of RAR windows corresponding to the plurality of RApreamble transmissions such that they do not overlap, transmission ofafter-mentioned identifier is unnecessary, so that the signaling amountcan be reduced.

In the embodiment 2-1, it may be permitted that the plurality of RARwindows corresponding to the plurality of RA preamble transmissionsoverlap. In this case, for example, the base station 20 includes, withinthe RAR or RA-RNTI (identifier indicating that the transmission signalis a RAR), an identifier for identifying which RACH resource subset(that is, which BS transmission beam) the RAR corresponds to. Theidentifier is, for example, an index for identifying basic broadcastinformation/SS, or an index for identifying the RACH resource subset.For example, when there is an overlapping time width between a RARwindow-A and a RAR window-B, even if the user apparatus 10 receives aRAR in the overlapping time width, the user apparatus 10 can determinewhich RACH resource subset the RAR corresponds to by the aboveidentifier. By allowing overlapping in this way, the whole time lengthof the RAR window can be shortened, so that delay can be reduced.

Embodiment 2-2

As shown in FIG. 12, in the embodiment 2-2, one RAR window is configuredcommonly to a plurality of RACH resource subsets corresponding todifferent BS transmission beams. For example, one RAR window isconfigured commonly for N (N is an integer equal to or greater than 1)RACH resource subsets. The value of N may be notified by a DCI, a MACsignal, a RRC signal and the like from the base station 20 to the userapparatus 10, may be preconfigured in the base station 20 and the userapparatus 10, or may be determined to be a value the same as a value(example: the number of BS transmission beams).

Also, for example, when the user apparatus 10 transmits a RA preambleusing at least one RACH resource subset in N consecutive RACH resourcesubsets, the user apparatus 10 monitors a RAR in the (common) RAR windowcorresponding to the N RACH resource subsets.

For example, as to a RA window for N RACH resource subsets, by setting,in the user apparatus 10, a time length (to be referred to as “offset”for convenience sake) from the end of the N RACH resource subsets in thetime direction to a start timing (time) of the RAR window, and a timelength (to be referred to as “window time length” for convenience sake)of the RAR window, the user apparatus 10 can determine the RAR windowbased on the offset and the window time length. Also, the base station20 holds the offset and the window time length, so that the base station20 can specify the RAR window that is used by the user apparatus 10based on the timing at which the RA preamble is received.

The above-mentioned offset and the window time length may be notified bya DCI, a MAC signal, a RRC signal and the like from the base station 20to the user apparatus 10, or, may be preconfigured in the base station20 and the user apparatus 10.

In the embodiment 2-2, one RAR window common to a plurality of RACHresource subsets is used, thus, for example, the base station 20includes, within the RAR or RA-RNTI, an identifier for identifying whichRACH resource subset (that is, which BS transmission beam) the RARcorresponds to. The identifier is, for example, an index for identifyingbasic broadcast information/SS, or an index for identifying the RACHresource subset. For example, even when the user apparatus 10 receives aRAR in one RAR window common to a plurality of RACH resource subsets,the user apparatus 10 can determine which RACH resource subset the RARcorresponds to.

Also, the order of the RACH resource subsets may be associated with theorder of RARs within the RA window. For example, as shown in FIG. 12, inthe case in which the user apparatus 10 transmits a RA preamble usingthe RACH resource subset B, and next, transmits a RA preamble using theRACH resource subset C, the user apparatus 10 determines that a RARreceived first in the RAR window common to these RACH resource subsetsis the RAR corresponding to the RACH resource subset B, and determinesthat a RAR received next to be a RAR corresponding to the RACH resourcesubset C.

In the above example, one RAR window is configured commonly for aplurality of RACH resource subsets. However, the technique is notlimited to this. A common RAR window may be configured for a pluralityof RACH resources used for RA preamble transmission by the userapparatus 10 among individual RACH resources included in a RACH resourcesubset. This is explained with reference to FIG. 12. For example, in acase where transmission of two RA preambles is performed using two RACHresources among a plurality of individual RACH resources included in theRACH resource subset indicated by B, one common RAR window is configuredcommonly for the transmission of the two RA preambles.

Also, in a case where one common RAR window is configured for aplurality of RACH resources used for RA preamble transmission, forexample, the base station 20 includes an identifier in a RAR or aRA-RNTI, for identifying which RACH resource the RAR corresponds to.

Like the embodiment 2-2, by using the RAR window common to a pluralityof RACH resource subsets, the whole time length of the RAR window can bedecreased, so that delay can be eliminated.

(Apparatus Configuration)

Next, an example of the functional configurations of the user apparatus10 and the base station 20 performing the above-mentioned operationsdescribed so far are described below. Each of the user apparatus 10 andthe base station 20 includes at least functions for implementing theembodiments 1 and 2. However, each of the user apparatus 10 and the basestation 20 may include only a part of functions in the embodiments 1 and2.

<User Apparatus>

FIG. 13 is a diagram illustrating an example of a functionalconfiguration of the user apparatus 10. As illustrated in FIG. 13, theuser apparatus 10 includes a signal transmission unit 101, a signalreception unit 102, a configuration information management unit 103, anda RA control unit 104. The signal reception unit 102 includes ameasurement unit 112 configured to measure a reception quality. Thefunctional configuration illustrated in FIG. 13 is only an example.Functional subdivision and names of the functional units are notparticularly limited as long as the operations associated with theembodiment can be performed. The signal transmission unit 101 and thesignal reception unit 102 may be referred to as a transmitter and areceiver respectively.

The signal transmission unit 101 generates a transmitting signal fromtransmission data to transmit the transmission signal by radio. Thesignal reception unit 102 receives by radio various signals, and obtainsa signal of upper layer from a received signal of the physical layer.Also, the signal transmission unit 101 is configured to executebeamforming in the transmission side, and the signal reception unit 102is configured to execute beamforming in the reception side.

The configuration information management unit 103 stores variousconfiguration information received from the base station 20 by thesignal reception unit 102. Content of the configuration information is,for example, information of thresholds, correspondence informationbetween beams and RACH resources subsets and the like described so far.Also, the configuration information management unit 103 storesconfiguration information preconfigured in the user apparatus 10.

The RA control unit 104 executes the processing of the random accessprocedure in the user apparatus 10 described in the basic example andembodiments 1 and 2. Note that a functional unit related to signaltransmission in the RA control unit 104 may be included in the signaltransmission unit 101 and a functional unit related to signal receptionin the RA control unit 104 may be included in the signal reception unit102.

Also, for example, the signal reception unit 102 is configured toreceive a plurality of predetermined signals transmitted from the basestation by a plurality of beams; and the signal transmission unit 101 isconfigured to transmit a preamble using a resource corresponding to atleast one beam of the plurality of beams, and the signal reception unit102 is configured to measure a reception quality for each of theplurality of beams, and the signal transmission unit 101 is configuredto transmit the preamble using a resource corresponding to a beam of areception quality that satisfies a predetermined condition.

The predetermined condition is, for example, that: the reception qualityis better than a predetermined threshold, or a difference between thereception quality and the best reception quality among receptionqualities of the plurality of beams is smaller than a predeterminedrelative threshold.

The signal transmission unit 101 may be configured to use resourcescorresponding to a predetermined upper limit number of beams of allbeams whose reception quality satisfies the predetermined condition soas to transmit the upper limit number of preambles.

The signal transmission unit 101 may be configured to performretransmission for a preamble transmitted by a first resource using asecond resource corresponding to a beam whose reception qualitysatisfies the predetermined condition.

The signal reception unit 102 may be configured to monitor a responsefor a preamble within a time window corresponding to a resource used fortransmitting the preamble by the signal transmission unit 101, or thesignal reception unit 102 may be configured to monitor a response forthe preamble within a time window common to a plurality of resourcesincluding a resource used for transmitting the preamble by the signaltransmission unit 101.

<Base Station 20>

FIG. 14 is a diagram illustrating an example of a functionalconfiguration of the base station 20. As illustrated in FIG. 14, thebase station 20 includes a signal transmission unit 201, a signalreception unit 202, a configuration information management unit 203 anda RA control unit 204. The functional configuration illustrated in FIG.14 is only an example. Functional subdivision and names of thefunctional units are not particularly limited as long as the operationsassociated with the embodiment can be performed. The signal transmissionunit 201 and the signal reception unit 202 may be referred to as atransmitter and a receiver respectively.

The signal transmission unit 201 includes a function configured togenerate a signal to be transmitted to the user apparatus 10 side, andto transmit the signal by radio. The signal reception unit 202 includesa function configured to receive various signals transmitted from theuser apparatus 10, and to obtain information of upper layer from thereceived signal. Also, the signal transmission unit 201 is configured toexecute beamforming in the transmission side, and the signal receptionunit 202 is configured to execute beamforming in the reception side.

The configuration information management unit 203 stores variousconfiguration information to be transmitted to the user apparatus 10.Content of the configuration information is, for example, thresholdinformation, correspondence information described so far. Also, theconfiguration information management unit 203 stores configurationinformation preconfigured in the base station 20.

The RA control unit 204 executes the processing of the random accessprocedure in the base station 20 described in the embodiments 1 and 2.Note that a functional unit related to signal transmission in the RAcontrol unit 204 may be included in the signal transmission unit 201 anda functional unit related to signal reception in the RA control unit 204may be included in the signal reception unit 202.

<Hardware Configuration>

The block diagrams (FIGS. 13 and 14) which are used above to describethe embodiments illustrate blocks in the units of functions. Thefunctional blocks (constituent units) are embodied in an arbitrarycombination of hardware and/or software. Means for embodying thefunctional blocks is not particularly limited. That is, the functionalblocks may be embodied by one unit in which a plurality of componentsare physically and/or logically coupled, or may be embodied by two ormore devices which are physically and/or logically separated and whichare connected directly and/or indirectly (for example, in a wired and/orwireless manner).

For example, the user apparatus 10 and the base station 20 according tothis embodiment may function as computers that perform the processesaccording to this embodiment. FIG. 15 is a diagram illustrating anexample of a hardware configuration of the user apparatus 10 and thebase station 20 according to this embodiment. The user apparatus 10 andthe base station 20 may be physically configured as a computer deviceincluding a processor 1001, a memory 1002, a storage 1003, acommunication device 1004, an input device 1005, an output device 1006,and a bus 1007.

In the following description, a word “device” may be referred to as acircuit, a device, a unit, or the like. The hardware configurations ofthe user apparatus 10 and the base station 20 may include one or moredevices indicated by reference numerals 1001 to 1006 in the drawing ormay not include some devices thereof.

The functions of the user apparatus 10 and the base station 20 arerealized by causing hardware such as the processor 1001 and the memory1002 to read predetermined software (a program) and causing theprocessor 1001 to perform calculation and to control communication ofthe communication device 1004 and reading and/or writing of data in thememory 1002 and the storage 1003.

The processor 1001 controls the computer as a whole, for example, byactivating an operating system. The processor 1001 may be constituted bya central processing device (CPU: central processing unit) including aninterface with peripherals, a control device, a calculation device, aregister, and the like.

The processor 1001 reads a program (program codes), a software module,or data from the storage 1003 and/or the communication device 1004 tothe memory 1002 and performs various processes in accordance therewith.As the program, a program causing a computer to perform at least a partof the operations described above in the embodiment is used. Forexample, the signal transmission unit 101, the signal reception unit102, the configuration information managing unit 103 and the RA controlunit 104 of the user apparatus 10 shown in FIG. 13 may be embodied by acontrol program which is stored in the memory 1002 and operated by theprocessor 1001. The signal transmission unit 201, the signal receptionunit 202, the configuration information management unit 203 and the RAcontrol unit 204 of the base station 20 shown in FIG. 14 may be embodiedby a control program which is stored in the memory 1002 and operated bythe processor 1001. Various processes described above have beendescribed to be performed by a single processor 1001, but may besimultaneously or sequentially performed by two or more processors 1001.The processor 1001 may be mounted as one or more chips. The program maybe transmitted from a network via an electric communication line.

The memory 1002 is a computer-readable recording medium and may beconstituted, for example, by at least one of a read only memory (ROM),an erasable programmable ROM (EPROM), an electrically erasableprogrammable ROM (EEPROM), and a random access memory (RAM). The memory1002 may be referred to as a register, a cache, or a main memory (a mainstorage device). The memory 1002 can store a program (program codes), asoftware module, or the like which can be executed to perform theprocesses according to the embodiment.

The storage 1003 is a computer-readable recording medium and may beconstituted, for example, by at least one of an optical disc such as acompact disc ROM (CD-ROM), a hard disk drive, a flexible disk, amagneto-optical disk (such as a compact disk, a digital versatile disk,or a Blu-ray (registered trademark) disk), a smart card, a flash memory(such as a card, a stick, or a key drive), a floppy (registeredtrademark) disk, and a magnetic strip. The storage 1003 may be referredto as an auxiliary storage device. Examples of the recording medium mayinclude a database including the memory 1002 and/or the storage 1003, aserver, and another appropriate medium.

The communication device 1004 is hardware (a transceiver device) thatallows communication between computers via a wired and/or wirelessnetwork and is referred to as, for example, a network device, a networkcontroller, a network card, or a communication module. For example, thesignal transmission unit 101 and the signal reception unit 102 of theuser apparatus 10 may be embodied by the communication device 1004. Thesignal transmission unit 201 and the signal reception unit 202 of thebase station 20 may be embodied by the communication device 1004.

The input device 1005 is an input device (such as a keyboard, a mouse, amicrophone, a switch, a button, or a sensor) that receives an input fromthe outside. The output device 1006 is an output device (such as adisplay, a speaker, or an LED lamp) that performs outputting to theoutside. The input device 1005 and the output device 1006 may beconfigured as a unified body (such as a touch panel).

The devices such as the processor 1001 and the memory 1002 are connectedto each other via the bus 1007 for transmitting and receivinginformation. The bus 1007 may be constituted by a single bus or may beconfigured by different buses for the devices.

The user apparatus 10 and the base station 20 may be configured toinclude hardware such as a microprocessor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a programmablelogic device (PLD), or a field programmable gate array (FPGA), or a partor all of the functional blocks may be embodied by the hardware. Forexample, the processor 1001 may be implemented by at least one hardwaremodule of these.

Summary of Embodiments

As described above, according to the present embodiment, there isprovided a user apparatus in a radio communication system including abase station and the user apparatus, including: a reception unitconfigured to receive a plurality of predetermined signals transmittedfrom the base station by a plurality of beams; and a transmission unitconfigured to transmit a preamble using a resource corresponding to atleast one beam of the plurality of beams, wherein the reception unitmeasures a reception quality for each of the plurality of beams, and thetransmission unit transmits the preamble using a resource correspondingto a beam of a reception quality that satisfies a predeterminedcondition.

According to the above configuration, a random access procedure to whichbeamforming is applied can be properly executed while avoidingperformance deterioration and avoiding giving interference.

The predetermined condition is, for example, that: the reception qualityis better than a predetermined threshold, or a difference between thereception quality and the best reception quality among receptionqualities of the plurality of beams is smaller than a predeterminedrelative threshold. According to this configuration using a threshold,accurate processing can be performed quickly.

The transmission unit may use resources corresponding to a predeterminedupper limit number of beams of all beams whose reception qualitysatisfies the predetermined condition so as to transmit the upper limitnumber of preambles. According to this configuration, since the numberof preambles can be restricted, for example, useless resource use can besuppressed.

The transmission unit may retransmit a preamble transmitted by a firstresource using a second resource corresponding to a beam whose receptionquality satisfies the predetermined condition. According to thisconfiguration, retransmission can be performed using proper resources.

The reception unit may monitor a response for a preamble within a timewindow corresponding to a resource used for transmitting the preamble bythe transmission unit, or the reception unit may monitor a response forthe preamble within a time window common to a plurality of resourcesincluding a resource used for transmitting the preamble by thetransmission unit. According to this configuration, the response for thepreamble can be monitored in a proper time window.

Complement of Embodiment

While embodiments of the invention have been described above, theinvention disclosed herein is not limited to the embodiments and it willbe understood by those skilled in the art that various modifications,corrections, alternatives, substitutions, and the like can be made.While description has been made using specific numerical value examplesfor the purpose of promoting understanding of the invention, suchnumerical values are only simple examples and arbitrary appropriatevalues may be used unless otherwise specified. The sorting of items inthe above description is not essential to the invention, detailsdescribed in two or more items may be combined for use if necessary, ordetails described in a certain item may be applied to details describedin another item (unless incompatible). Boundaries between functionalunits or processing units in the functional block diagrams cannot besaid to be necessarily correspond to boundaries of physical components.Operations of a plurality of functional units may be physicallyperformed by one component, or an operation of one functional unit maybe physically performed by a plurality of components. The processingsequences described above may be changed in the order as long as theyare not incompatible with each other. For the purpose of convenience ofdescription, while a user apparatus 10 and a base station 20 have beendescribed above with reference to functional block diagrams, suchapparatuses may be embodied by hardware, by software, or by combinationthereof. Each of software which is executed by a processor of the userapparatus 10 and software which is executed by a processor of the basestation 20 in the embodiments of the invention may be stored in anappropriate storage medium such as a random access memory (RAM), a flashmemory, a read only memory (ROM), an EPROM, an EEPROM, a register, ahard disk (HDD), a removable disk, a CD-ROM, a database, or a server.

Notification of information is not limited to the aspects/embodimentsdescribed in this specification, but may be performed using othermethods. For example, the notification of information may be performedphysical layer signaling (such as downlink control information (DCI) oruplink control information (UCI)), upper layer signaling (such as radioresource control (RRC) signal, medium access control (MAC) signaling, orbroadcast information (master information block (MIB) and systeminformation block (SIB))), other signals, or combinations thereof. TheRRC signaling may be referred to as an RRC message and may be, forexample, an RRC connection setup message or an RRC connectionreconfiguration message.

The aspects/embodiments described in this specification may be appliedto systems employing long term evolution (LTE), LTE-advanced (LTE-A),SUPER 3G, IMT-Advanced, 4G, 5G, future radio access (FRA), W-CDMA(registered trademark), GSM (registered trademark), CDMA2000, ultramobile broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, ultra-wideband (UWB), Bluetooth (registered trademark), or otherappropriate systems and/or next-generation systems to which the systemsare extended.

The processing sequences, the sequences, flowcharts and the like of theaspects/embodiments described above in this specification may be changedin the order as long as they are not incompatible with each other. Forexample, in the methods described in this specification, various stepsas elements are described in an exemplary order and the methods are notlimited to the described order.

Specific operations which are performed by the base station 20 in thisspecification may be performed by an upper node thereof in some cases.In a network including one or more network nodes including a basestation 20, various operations which are performed to communicate with auser apparatus 10 can be apparently performed by the base station 20and/or network nodes (for example, an MME or an S-GW can be consideredbut the network nodes are not limited thereto) other than the basestation 20. A case in which the number of network nodes other than thebase station 20 is one has been described above, but a combination ofplural different network nodes (for example, an MME and an S-GW) may beused.

The aspects described in this specification may be used alone, may beused in combination, or may be switched with implementation thereof.

The user apparatus 10 may also be referred to as a subscriber station, amobile unit, a subscriber unit, a wireless unit, a remote unit, a mobiledevice, a wireless device, a wireless communication device, a remotedevice, a mobile subscriber station, an access terminal, a mobileterminal, a wireless terminal, a remote terminal, a handset, a useragent, a mobile client, a client, or several appropriate terms by thoseskilled in the art.

The base station 20 may be referred to as an NodeB (NB), an enhancedNodeB (eNB), a gNB, a base station, or some other appropriate terms bythose skilled in the art.

The terms “determining (determining)” and “deciding (determining)” usedin this specification may include various types of operations. Forexample, “determining” and “deciding” may include deeming that toperform judging, calculating, computing, processing, deriving,investigating, looking up (e.g., search in a table, a database, oranother data structure), or ascertaining is to perform “determining” or“deciding”. Furthermore, “determining” and “deciding” may includedeeming that to perform receiving (e.g., reception of information),transmitting (e.g., transmission of information), input, output, oraccessing (e.g., accessing data in memory) is to perform “determining”or “deciding”. Furthermore, “determining” and “deciding” may includedeeming that to perform resolving, selecting, choosing, establishing, orcomparing is to perform “determining” or “deciding”. Namely,“determining” and “deciding” may include deeming that some operation isto perform “determining” or “deciding”.

An expression “on the basis of ˜” which is used in this specificationdoes not refer to only “on the basis of only ˜,” unless apparentlydescribed. In other words, the expression “on the basis of ˜” refers toboth “on the basis of only ˜” and “on the basis of at least ˜.”

So long as terms “include” and “including” and modifications thereof areused in this specification or the appended claims, the terms areintended to have a comprehensive meaning similar to a term “comprising.”A term “or” which is used in this specification or the claims isintended not to mean an exclusive or.

In the entire disclosure, for example, when an article such as a, an, orthe is added in translation into English, such an article refers toincluding the plural unless otherwise recognized from the context.

While the invention has been described above in detail, it is apparentto those skilled in the art that the invention is not limited to theembodiments described in the specification. The invention can be carriedout as modified and changed embodiments without departing from theconcept and scope of the invention which are defined by the appendedclaims. Accordingly, the description in this specification is made forillustrative description and does not have any restrictive meaning.

This patent application is based upon and claims the benefit of priorityof Japanese Patent Application No. 2017-019142 filed on Feb. 3, 2017,and the entire contents of Japanese Patent Application No. 2017-019142are incorporated herein by reference.

LIST OF REFERENCE SYMBOLS

-   10 user apparatus-   101 signal transmission unit-   102 signal reception unit-   112 measurement unit-   103 configuration information management unit-   104 RA control unit-   20 base station-   201 signal transmission unit-   202 signal reception unit-   203 configuration information management unit-   204 RA control unit-   1001 processor-   1002 memory-   1003 storage-   1004 communication device-   1005 input device-   1006 output device

The invention claimed is:
 1. A terminal comprising: a transceivercoupled to a processor that measures power of synchronization signalblocks received from a base station, wherein the processor selects asynchronization signal block with measured power above a threshold,wherein the transceiver transmits a preamble using a resourcecorresponding to the selected synchronization signal block, and whereinthe transceiver performs retransmission for preamble transmission thatuses the resource, the retransmission being performed using anotherresource corresponding to the selected synchronizations signal block oranother synchronization signal block with measured power above thethreshold.
 2. A terminal comprising: a transceiver coupled to aprocessor that measures power of synchronization signal blocks receivedfrom a base station, wherein the processor selects a synchronizationsignal block with measured power above a threshold, wherein thetransceiver transmits a preamble using a resource corresponding to theselected synchronization signal block, and wherein responsive todetermining that random access response reception by the transceiver fora preamble transmitted using the resource is not successful, thetransceiver performs another preamble transmission using anotherresource corresponding to the selected synchronization signal block oranother synchronization signal block with received power above thethreshold.
 3. The terminal as claimed in claim 1, wherein thetransceiver receives the threshold from the base station.
 4. Theterminal as claimed in claim 3, wherein the synchronization signal blockincludes a synchronization signal and a broadcast channel.
 5. Theterminal as claimed in claim 1, wherein the synchronization signal blockincludes a synchronization signal and a broadcast channel.
 6. Theterminal as claimed in claim 2, wherein the transceiver receives thethreshold from the base station.
 7. The terminal as claimed in claim 2,wherein the synchronization signal block includes a synchronizationsignal and a broadcast channel.
 8. A base station comprising: atransmitter that transmits synchronization signal blocks; and a receiverthat receives a preamble transmitted by a terminal using a resourcecorresponding to a synchronization signal block with measured powerabove a threshold, wherein the receiver receives a preamble byretransmission for preamble transmission that uses the resource, theretransmission being performed using another resource corresponding tothe synchronization signal block or another synchronization signal blockwith measured power above the threshold.
 9. A base station comprising: atransmitter that transmits synchronization signal blocks; and a receiverthat receives a preamble transmitted by a terminal using a resourcecorresponding to a synchronization signal block with measured powerabove a threshold, wherein responsive to determining that random accessresponse transmission by the transmitter for a preamble received usingthe resource is not successful, the receiver performs another preamblereception using another resource corresponding to the synchronizationsignal block or another synchronization signal block with received powerabove the threshold.
 10. A radio communication method for a terminalcomprising: measuring power of synchronization signal blocks receivedfrom a base station; selecting a synchronization signal block withmeasured power above a threshold; transmitting a preamble using aresource corresponding to the selected synchronization signal block; andperforming retransmission for preamble transmission that uses theresource, the retransmission being performed using another resourcecorresponding to the selected synchronization signal block or anothersynchronization signal block with measured power above the threshold.11. A radio communication method for a terminal comprising: measuringpower of synchronization signal blocks received from a base station;selecting a synchronization signal block with measured power above athreshold; and transmitting a preamble using a resource corresponding tothe selected synchronization signal block, wherein responsive todetermining that random access response transmission for a preamblereceived using the resource is not successful, another preamblereception is performed using another resource corresponding to theselected synchronization signal block or another synchronization signalblock with received power above the threshold.